FYI, How to pass touch events to UIWebView

bharath2020 · April 2009

I was wondering how to pass touch events to UIWebview and here it is

UIWebview does not handle the touch event, instead it is some other view (i.e UIWebDocumentView) which handles the events. But, many people wonder, including me, how this undocumented, private object come into picture.

And the answer is UIWebview seems to override the hitTest:withEvent: method which on invoked returns the UIWebDocumentView, which means that all the subsequent touch events will be routed to UIWebDocumentView

Now how do we by pass this situation, so that one of our view class should get control over the touch event?

This can be done by subclassing the UIWebview and overriding the hitTest:withEvent method and invoking super class method



-(void)hitTest:(CGPoint)point withEvent:(UIEvent*)event
{
    _responderView = [super hitTest:point withEvent:event];//capture the view which actually responds to the touch events

   return self;//pass self so that the touchesBegan,touchesMoved and other    events will be routed to this class itself
   
}


//override touch events
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
  [ _responderView touchesBegan:touches  withEvent:event];
}

Hope this helps

pulaskeet · November 2009

A+ post, worked well for me. This is a very efficient way of doing this, since many posts refer to private APIs which are grounds for App Rejection.

pulaskeet · November 2009

After I implemented the overridden hitTest method, I ran into a few problems. Namely, the responderView wouldn't receive any messages after touchesBegan, which made me think that there were some private methods being called that we aren't allowed to interact with.

The natural (and legitimate) way to deal with these private methods is to setup a dummy class that forwards any invocation methods to the actual responder class. To get a clear idea of what I'm talking about, look up the forwardInvocation method in the NSObject Class Reference.

Below is the solution that gave me 100% control over any methods I wanted, while steering clear of private APIs and method swizziling.



@interface ResponderWrapper : NSObject {
	UIView *responderView;
}

- (id)initWithResponderView:(UIView*)aResponderView;
@end

@implementation ResponderWrapper

- (id)initWithResponderView:(UIView*)aResponderView {
	if (self = [super init]) {
		responderView = [aResponderView retain];
	}
	return self;
}

- (void)dealloc {
	[responderView release];
	[super dealloc];
}

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
	[responderView touchesBegan:touches withEvent:event];
	NSLog(@\"touches began\");
}

- (BOOL)respondsToSelector:(SEL)aSelector {
	return [responderView respondsToSelector:aSelector];
}

- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector {
    return [responderView methodSignatureForSelector:aSelector];
}

- (void)forwardInvocation:(NSInvocation *)anInvocation {
	if ([responderView respondsToSelector:anInvocation.selector]) {
		[anInvocation invokeWithTarget:responderView];
	}
}

@end

@implementation DLWebView

- (UIView*)hitTest:(CGPoint)point withEvent:(UIEvent*)event {
	UIView *responderView = [super hitTest:point withEvent:event];
	return [[[ResponderWrapper alloc] initWithResponderView:responderView] autorelease];
}

@end

DLWebView is nothing more than a subclass of UIWebView, and for simplicity I defined the wrapper object in the same class.

bharath2020 · November 2009

You have to override all the touches event from Began,Moved,Cancel,Ended and then route to the Private view or the ResponderView..

But your solution of forward invocation is a class which eliminates the need to override the methods even if some new one are added in future, and hence Bug free..

Thanks for sharing it..

kidzx · February 2010

First off excellent method to intercept touches on UIWebview. I suddenly have problem when using two fingers to pinch zoom , the web doesnt get re-rendered. Do you guys face the same problem?

johnlikesit · March 2010

pulaskeet;145250 said:
....

Do you have any tips for my on how do I implement this with my app :)

Thanks!

reecon · July 2010

How to use that code, do you have some example implementation for it? thanks :)

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